Volcanic Ash Closes Airports Across Indonesia

Passengers queue up at the international terminal at Bali's Ngurah Rai airport in Denpasar for information of flight delays due to volcanic ash near Indonesia's resort island on July 10, 2015. Ash drifting from an Indonesian volcano closed five airports on July 10, including the one on the holiday island of Bali, causing about 250 flights to be cancelled and stranding thousands of holidaymakers. The international airport on nearby popular Lombok island was also among those closed late on July 9 as Mount Raung in East Java province spewed clouds of ash. AFP PHOTO / SONNY TUMBELAKA (Photo credit should read SONNY TUMBELAKA/AFP/Getty Images)

SONNY TUMBELAKA/AFP/Getty Images

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Volcanic Ash Closes Airports Across Indonesia

Passengers queue up at the international terminal at Bali's Ngurah Rai airport in Denpasar for information of flight delays due to volcanic ash near Indonesia's resort island on July 10, 2015. Ash drifting from an Indonesian volcano closed five airports on July 10, including the one on the holiday island of Bali, causing about 250 flights to be cancelled and stranding thousands of holidaymakers. The international airport on nearby popular Lombok island was also among those closed late on July 9 as Mount Raung in East Java province spewed clouds of ash. AFP PHOTO / SONNY TUMBELAKA (Photo credit should read SONNY TUMBELAKA/AFP/Getty Images)

This damage is due to the nature of volcanic ash. It is really just tiny, airborne glass shards that melt at temperatures found in modern jet engines. This means when the ash cools in the engines, it coats and blocks important parts of the engines, causing the engines to shut down. We know this thanks to incidents where jets have actually flown through ash plumes unknowingly and experienced just that. Luckily, they were able to recover so they could land safely, although the aircraft sustained extensive damage to their engines and glass.

Right now, where there is a threat of volcanic ash to aircraft, pilots turn to Volcanic Ash Advisory Centers (VAAC). They monitor ash to issue statements and maps about potential ash hazards to aircraft, dividing the world up into different zones that are watched by a series of VAAC offices. For example, the current eruption at Ruang is under the domain of the VAAC based in Darwin. Across North America, an eruption from the Cascades would fall under the Washington VAAC while the Aleutians are covered by the Anchorage VAAC. The VAACs are needed because volcanic ash doesn't appear in most air traffic control radar systems, so aircraft likely have no idea they are entering volcanic ash unless the plume is thick enough to be noticed visually.

The typical VAAC statement (see below) contains information about the flight level that ash is likely to be found, the overall location of the plume and some forecasts about how it might move in elevation and location due to weather. They also usually include information about the sources of the information about the plume, such satellite images, pilot reports or ground reports. These reports help airlines decide how to reroute or cancel their flights if a volcanic eruption is underway.

What exactly are the threats caused by volcanic ash to aircraft? Beyond the threat of engine stall, pilots are told that ash and "smoke" (actually sulfur dioxide gas) could get into the cockpit, St. Elmo's Fire could appear, fire warnings may occur in forward cargo holds and pitot tubes could be blocked, causing incorrect flight speed information. The ash itself is highly abrasive, so flying through ash will damage the leading edge and windshield of the aircraft's cockpit. Landing at airports coated in ash can cause runways to become slippery as well, so caution needs to be taken. The biggest problem is that a lot of the ways to avoid the hazards of volcanic ash are very different than how pilots avoid severe weather hazards.

Due to this difference, the FAA offers some suggestions of how to deal with volcanic ash. Ground operations are told to tell aircraft to try to avoid the ash along with warning that if there is ash on the ground, aircraft will kick up a lot of the ash. In flight training manuals, pilots are told that "it is recommended that pilots encountering an ash cloud should immediately reduce thrust to idle (altitude permitting), and reverse course in order to escape from the cloud." This is based on the experience of other aircraft that have encountered ash. Beyond this, the International Civil Aviation Organization released a report called "Flight Safety and Volcanic Ash" after the 2010 Eyjafjallajökull eruption that offers advice on risk management during a volcanic event.

That being said, there is very little regulation in the United States for how the FAA will respond to a volcanic ash crisis. The assumption is that, much like after 9/11, the FAA can close airspace to all civilian air traffic. However, much like what happened in Europe, a prolonged closure will bring the wrath of airlines and passengers. Although the Cascades are quiet right now, it is inevitable that another explosive eruption will occur, so planning for how we will respond to an eruption is vital, especially in a country where air travel is so important.

*Don't confuse Raung with another Indonesian volcano called Ruang (I know I did).